In a file system virtualization environment, a Network File System (NFS) protocol assigns a unique Transaction ID (XID) to each requested operation from a client device to a file server device. The XID is generated by the client device when issuing the request, whereby the XID is returned by the server in the server response to the client device. An application layer gateway device is utilized to multiplex requests between multiple clients and one or more file servers, whereby the gateway maps the XIDs received from the client devices into new, unique Transaction ID (XID′) values before forwarding the client devices' requests to the server(s). The gateway device must save the mapping information between the client device and the XID by using the identity of the client device (i.e. its network address) and XID. Further, the gateway device must also map its created XID′ to the client device. When the server returns a response with the XID′, the gateway device maps the received XID′ back to the originating client identity and XID. Therefore, the gateway device must save and retrieve the original XID included in the client device's request to be able to include it in the server response that is ultimately sent back to the client device. Accordingly, the gateway device must store corresponding XID/XID′ entries for every operation in progress in a mapping table.
Further, some protocols, including the NFS protocol, use the XID information to identify operations that are duplicates of prior operations that are being retried due to timeouts or other errors. The application gateway device must therefore map a retransmitted operation for a client device's XID to the same XID′ used the first time the operation was proxied by the gateway device. This ensures the server detects this request as a retransmitted request instead of a new request. Considering that the gateway device must store the XID/XID′ information for every operation in a mapping table, and that client devices are capable of sending thousands of requests per second, the mapping table used by the gateway device can easily grow to millions of entries. Further, if the gateway device utilizes a backup gateway device, the mapping table must also be stored in a shared memory and replicated in the backup gateway device so that the backup device can seamlessly handle communications in case the active gateway device goes off-line. This current implementation imposes a significant burden on the active and backup gateway devices.
What is needed is a file virtualization device which algorithmically generates a server side transaction identifier (XID′) and replicates the algorithm among one or more virtualization devices without requiring the needed amount of substantial storage space to store XID/XID′ mapping information.